1. Field
The invention relates to a highly sensitive method for the detection of differences between the physically measurable properties of a sample and a reference.
The invention relates in particular to a method for the detection of the change in a physically measurable property of a sample brought about by an environmental influence.
2. Description of Related Art
For the industrial production of dyes, pigments, coatings, UV stabilizers and sun protection agents, it is of critical importance to know the light fastness of the products. At the present time, the light fastness of a product is measured by the product being irradiated with light of which the spectral distribution corresponds to that of sunlight on the surface of the earth. Following irradiation, the color change is quantified with the aid of reference systems. The disadvantage with this procedure is the to some extent very long irradiation times which are necessary in order to make a color change detectable in many products. For example, according to the relevant DIN Standards, the irradiation times are 1000 hours and more. For very light-fast samples, they are 10 to 50 years. A reference is then made against a color scale, for example the blue wool scale. The disadvantage with this procedure is, furthermore, that a human being has to make the assessment and this assessment is therefore determined by a subjective impression.
Examples of samples which need particularly long exposure times are façade paint, express highway signs, sealing materials for buildings, electrical insulators, roof tiles and safety panels. Further samples are mentioned in the standards below for exposure and weathering.
Relevant standards for weathering with artificial daylight are ISO 4892 (1994) for plastics, ISO 11341 (1994) for coatings and paints, ISO 11507 (1997) for coatings in instruments, ISO 3917 (1999) for road vehicle safety panels, ISO 11431 (2002) for civil engineering joint sealing materials, ISO 105-B02 (1994) for textile color fastness checks and ISO 105-B04 (1994) for textile color fastness weathering.
Relevant standards for direct weathering are ASTM G7, ISO 877, ISO 2810, ASTM D4141C (Black Box) and ASTM G24 (exposure under glass).